The decomposition or decay of organic matter is a natural process which is accomplished by bacteria and fungi. The decay or oxidation-reduction process requires a food supply in the form of carbon, nitrogen and vitamins, plus an adequate supply of oxygen. An oxidation bioreactor must, therefore, breathe, i.e., oxygen must enter and carbon dioxide must be exhausted from the bio-reactor. If there is insufficient oxygen to sustain the aerobic bacteria they will be replaced by anaerobic, non-oxygen consuming bacteria, and the decomposition process will slow and become incomplete, i.e., a residue of sludge will be left which must be further processed.
In the aerobic decay process the bacterial decomposition of organic matter is carried out by successive strains of bacteria which are activated at different temperatures. In a batch operation the decay process is initiated by cool-temperature bacteria known as psychrophiles which function best at about 45-55.degree. F. They attack the organic matter and burn off or oxidize the carbon compounds, thus producing heat as a by-product. A rise in temperature, either from bacterial activity or higher atmospheric temperature, will activate strains of warm-temperature bacteria called mesophiles which are most active at 70-90.degree. F. The mesophiles feed with such intensity that they raise the ambient temperature to a point where the environment within the reactor is no longer compatible to them. This occurs at about 104.degree. F., where high-temperature bacteria called thermophiles are activated. The thermophiles then raise the ambient temperature until it stabilizes at approximately 158.degree. F. where they complete their work. The decaying material will then return to near normal atmospheric temperature and the mesophiles become active again until bacterial decomposition is nearly complete. While the bacterial decomposition is taking place, a wide variety of other micro-organisms are at work in the decaying material. For instance, psychrophilic, mesophilic and thermophilic fungi help break down cellulose and lignin during all of the temperature phases of the process. Actinomycetes, which are part bacteria and part fungi, clean up after the bacteria by consuming the tough cellulose, starches, proteins and lignin. In addition, enzymes, which are produced by bacteria, remain active in reducing the toughest constituents of the compost long after the parent bacteria have died.
In a typical garden composting effort, vegetation and food scraps are deposited in a pile which is aerated periodically by manually turning the material with a garden fork. This process is laborious, slow and annoying since it takes upward of six months to complete and the decaying material produces odors and attracts flies and other pests. Commercial batch composters have been proposed to contain or enclose the composting process within a cylindrical tank which has been mounted on rollers for rotation. The tank is typically loaded with organic material to approximately one-half of its volume. In such a composter the decaying material, and the associated odors, are confined within the tank where the material is protected from pests and then aerated or tumbled by periodic turning of the tank itself. Such devices are an improvement over the well known compost piles, since they limit the physical labor required while removing the annoyance of odors and pests and they reduce the time required to compost a batch of material to between two and four weeks.